ALBERT

Description: :  The Upper Campanian Canyon Creek Member of the Ericson Formation in the Greater Green River Basin of southern Wyoming, USA, is a regionally extensive sandstone sheet of fluvial origin. A well-log and outcrop dataset allows this ancient fluvial system to be examined basin-wide, covering an area of approximately 45,000 km 2 . Changes in fluvial style and architecture, and in thickness and net-to-gross occur both down-dip and along strike, across the whole fluvial system, allowing insight on both local and regional structural styles in the basin. From the proximal reaches of the system in the west and northwest to the distal areas in the east and southeast, the Canyon Creek Member (and its equivalents) shows a first-order trend of thickening and of net-to-gross reduction, as well as a change of planform style from braided to meandering. The reason for these trends is an eastward increase of subsidence away from the orogenic belt, probably resulting from reduced activity in the Sevier fold–thrust belt, which decreased the importance of the tectonic loading and flexural subsidence and enhanced the signal of the dynamic subsidence. The Laramide orogeny is typically thought to have been initiated during the Maastrichtian or Paleocene. However, study of the Canyon Creek Member strongly indicates earlier initiation during the Campanian. The above general proximal-to-distal trends in the Canyon Creek are locally modified by early differential movement across the Rock Springs Uplift, the Uinta Mountains, the Rawlins Uplift, and the Sierra Madre Uplift, all of which are Laramide-style structures. This early movement is shown by reduced thickness and increased net-to-gross over the crest of these structures and by the opposite trend down-flank on the structure into the footwall of the adjacent structure. This asymmetric pattern of thickness and net-to-gross development within individual Canyon Creek "subbasins" is the typical and distinctive Laramide basin signature. The Canyon Creek Member of the Ericson Formation is a clear example of how varied a fluvial system can be laterally in response to minute changes in accommodation, slope, and other parameters, and illustrates how important it is to recognize that variability before embarking in the more complicated task of recognizing these changes through time in a sequence stratigraphic framework.

Description: Deltas are sensitive indicators of coastal processes (e.g., waves and tides) and show dynamic changes in shoreline morphology, distributary channel network, and stratigraphic architecture in response to coastal forcing. Numerical modeling has long been used to show delta evolution associated with a single dominant coastal process, but rarely to examine the sensitivity of deltas to mixed processes. Physics-based morphodynamic simulations (Delft3D) are used to investigate the influence of tidal currents on deltas. Tidal amplitude and the sand:mud ratio of subsurface sediment have been varied in the model. The results show that increasing tidal amplitude causes deeper and more stable distributary channels and more rugose planform shoreline patterns. A new metric for channel geometry quantifies tidal influence on the distributary channel network. Stable distributary channels act as an efficient mechanism for ebb-enhanced currents to (1) bypass sediment across the delta plain, and (2) extend channel tips seaward through mouth bar erosion. The basinward channel extension leads to sandier deposits in the tide-influenced deltas than in their river-dominated counterparts. The delta-front bathymetry also reflects sediment redistribution, changing the delta-front profile from concave to convex with compound geometries as tidal amplitude increases. These results suggest that channel overdeepening is a possible tidal signature that should be considered when interpreting ancient systems, and that sand may be bypassed much farther basinward in tide-influenced than in purely river-dominated deltas.

Description: Understanding the relationship between sedimentation and tectonics is critical to the analysis of stratigraphic evolution in foreland basins. Previous models of foreland basins have explained stratal development, but were done generally under the assumption that steady allogenic forcing produces a steady stratigraphic response. They did not consider autogenic shoreline behaviour during the development of the subsidence pattern characteristic of foreland basins. We present a mathematical model and flume experiments that explore how subsidence and sediment-supply rates control the shoreline trajectory and the stratal patterns that fill foreland basins. Through these models, we found differing autogenic responses in the rate and direction of shoreline migration, and these generated three distinct styles of stratal architecture, despite the constant external forcing (i.e. constant sediment discharge and basin substrate tilting). The first response was 'autoretreat', where shoreline migration switched from initial progradation to retrogradation. The second response was progradation followed by constant aggradation of the shoreline. The third response was maintained progradation with a markedly accelerating rate. We termed this latter newly observed autogenic behaviour 'shoreline autoacceleration'. These three modes of shoreline behaviour and their accompanying stratal architecture provide a basic framework for the relationship between sedimentation and tectonic activity in foreland basins under the simplified conditions presented here. © 2013 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.